The magnetic disk drive unit adapted for writing and reading of data on a rotating ferromagnetic medium, i.e., magnetic disk by scanning a magnetic head thereon is widely used in the modern information society as the major storage device. The magnetic head is carried on a slider, which is kept afloat on the magnetic disk with a gap of the nanometer order during the writing/reading operation. A drive force for moving the magnetic head to a selected position is typically produced by a voice coil motor (VCM). The voice coil motor includes a coil which is coupled to a pivoted arm, which is coupled to a magnetic head slider via a suspension including a load beam and a gimbal. The load beam is a spring for generating a load in balance with the float quantity of the slider. The gimbal is a spring for supporting the slider and allowing for elastic deformation in planes other than the plane parallel to the disk surface, for accommodating disk axial run-outs and inclinations associated with assembly without detracting from the tracking fidelity. This structure permits the magnetic head to be moved to the selected track on the rotating disk while maintaining a stable state.
Recent efforts are being made to increase the recording density of magnetic disk drive units to a higher level and hence, to reduce the track width. Since the magnetic head must be accurately positioned to such a narrow track, there is a need for improving the precision of head positioning. In the prior art, the head positioning is performed solely by large actuators such as voice coil motors as mentioned above, which lack sufficient precision to comply with the narrowing of track width. For high recording density disk drive units, high precision positioning mechanisms or micro-actuators are essentially needed.
In JP-A 2004-213818, 2004-213819 and 2004-213820, the inventors proposed a micro-actuator capable of high precision positioning utilizing electromagnetic force. In the micro-actuator, two plate springs, referred to as micro-beams, are used to couple rotor and stator sections. The micro-beams are formed integrally with the gimbal of the suspension, by bending.
Each micro-beam is of generally rectangular shape having a high aspect ratio and has a reduced gage in a tracking direction and an increased gage in a perpendicular direction, i.e., the direction in which the suspension load beam applies a load to the magnetic head slider. Then the micro-beams support the rotor for allowing swing motion of the rotor in the tracking direction and maintains high stiffness in the load direction. A permanent magnet and a coil are disposed in the rotor and stator sections, respectively, to construct a second stage of voice coil motor for achieving controlled high-precision positioning in the track transverse direction. The type of this micro-actuator is referred to as “slider drive type,” hereinafter, because the slider is driven via the gimbal.
As a result of performance improvement, the magnetic disk drive unit now finds wide-spreading applications in various fields including video image recording apparatus and car navigation systems. For small-size magnetic disk drives using magnetic disks having a diameter of less than 2.5 inches, studies have been made to incorporate them in portable equipment including digital still cameras, video cameras and audio players, and some are used in practice. In such applications, the impact resistance of the drive unit is important. Possible countermeasures for impact safe-guard, now under research and development, include a weight reduction of the overall drive unit, a casing having a damping structure, a size reduction and shape design of the slider, and a controlled structure for avoiding impact.
In the slider drive type micro-actuator the inventors previously proposed, the micro-beams are dimensioned about 0.03 mm by about 0.005 mm in cross section and are sometimes prone to deformation by strong impact. The micro-beams can be ruggedized and stiffened by increasing their cross-sectional area, but the spring constant of micro-beams in the tracking direction is also increased, posing a need to increase the volume of permanent magnet and coil. Simply increasing the weight of the suspension distal end, however, results in a lower resonance frequency and an increased inertia moment, which make the control by the coarse-adjustment actuator difficult, failing to increase the precision of head positioning by two stage actuators. For this reason, it is difficult to apply the slider drive type micro-actuator to portable recording equipment.
The references pertinent to the technology of the present invention include U.S. Pat. No. 6,295,185; U.S. Pat. No. 6,078,473; Fan et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 1000-1005; Koganezawa et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 35, No. 2, March 1999, pp. 988-992; and Koganezawa et al., IEEE TRANSACTIONS ON MAGNETICS, Vol. 32, No. 5, September 1996, pp. 3908-3910.